The present invention relates to magnetic brush development apparatus for applying developer material to a latent image on a photoconductor, and more particularly to improved means for feeding and delivering developer material to the magnetic brush. The magnetic brush apparatus can be used in an electrographic copier/duplicator, for example.
Magnetic brush development apparatus are well known in the art. Such apparatus may include a housing having a sump which receives developer material. When the developer material comprises a mixture of carrier particles and smaller toner particles, the material is mixed in the sump to triboelectrically charge the material prior to delivering it to a developer roller where it can be transferred to an electrostatic image on a photoconductor.
It is desirable to minimize the size of the development apparatus. Such enables a reduction in the overall size of the copier/duplicator or allows addition of other equipment within the same space. Also, color copiers require a plurality of magnetic brush development apparatus at the development station in order to provide toner of different colors to the photoconductor. As many as four development stations may be required in order to provide black toner and three colored toners to a photoconductor. The need for as many as four development apparatus in the development station can require a copier/duplicator to be quite large unless each of the development apparatus in the development station is very compact.
A developer material having permanent magnet carrier particles is disclosed in commonly assigned U.S. Pat. No. 4,546,060 issued Oct. 8, 1985 in the names of E. T. Miskinis and T. A. Jadwin, and entitled "Two-Component, Dry Electrographic Developer Compositions Containing Hard Magnetic Carrier Particles and Method for Using the Same." The magnetic carrier particles in such material have a tendency to cling together to form clumps and, in general, in the absence of an external field, such materials have a tendency to behave somewhat like wet sand due to the magnetic attraction exerted between the particles. Such a material creates special problems in mixing developer material, circulating the material through the development station, agitating and shearing the developer to promote triboelectric charging, and in feeding the developer material to a magnetic brush.
Commonly assigned U.S. patent application Ser. No. 597,323, filed Apr. 6, 1984 in the names of B. J. Joseph and T. K. Hilbert entitled "Electrographic Development Apparatus Having A Ribbon Blender" discloses development apparatus particularly suitable for use with development material having permanent magnetic carrier particles as disclosed in U.S. Pat. No. 4,546,060. More particularly, the apparatus disclosed in application Ser. No. 597,323 includes a ribbon blender that is used for mixing, feeding and triboelectrically charging such material in the sump of a developer station, and a magnetic feed roller that transfers material from the sump to a magnetic brush. A relatively large area is available for transfer of the developer material from the magnetic feed roller to the magnetic brush. Thus a reservoir for developer material is provided near the magnetic brush so that there is a continuous and uninterrupted supply of developer material in that area.
In some instances it is desirable to control the flow of developer material to a magnetic brush, e.g., to turn the flow on or off. This can be accomplished by delivering the material to the brush through a narrow slot that can be closed to shut off the flow of material to the brush. A feed slot effectively eliminates the developer reservoir near the magnetic brush, and requires a continuous and uninterrupted supply of developer material through the slot Also, any excess developer material in the area of the slot should be removed from the area of the slot and returned to the sump to avoid overfeeding of developer material and jamming of the apparatus.